In general, there have been known such a figure processing apparatus and a method that a figure is drafted and edited in response to an instruction issued from an operator with operating a mouse or the like, while observing the figure displayed on a display. When the figure is formed by way of the above-explained apparatus and method, figure processings such as a parallel displacement, a rotation, a mirror-image inversion, a duplication, an erasing and a zooming operation must be carried out with respect to the figure displayed on the display. These figure processings may require to move the figure shown in the display to a desirable position, to designate a side or a radius of the figure, and to modify it to a desirable length. However, it is difficult that the operator visually and correctly measures a distance and a position on a display screen. It is also difficult to make a pointing device such as a mouse coincident with a desirable pixel, because the operator may move his hand. As described above, it is so difficult for the operator to correctly designate a point, a position and a length on a screen of a display.
Therefore, most of the drafting or figure processing apparatuses aided by display devices own a function to display square latticed rules on the screens and also to correct the position pointed out by the pointer on the display screen to a cross point of the lattice or a point on the lattice line in order to aid the position designation for accepting such demands.
The operators who employ such a figure processing apparatus, can readily determine a correct position by designating an adjoining position of a target lattice point or lattice line, instead of pointing the exact point on the display.
Some of these figure processing apparatuses own a function capable of modifying an interval of the lattice lines, a gradient thereof, and a datum position by the operator.
However, since the conventional figure processing apparatuses can display only the square latticed rules, it is impossible to determine correct lengths when the lines cross each other not at a right angle. Also, since it is not easy to modify an attribute of the ruled lattice in the conventional figure processing apparatuses, it is difficult to locate a lattice point of the rules on the center of the circle for correctly modifying the center and radius of the circle based on the rules. Also, in case that the figure is desirable to be moved in a proper direction, it is difficult to make the gradient of the latticed rules coincident with the desirable direction for relying to move the figure on the rules.
For instance, if a designation is made of a point which is separated from a certain point by a predetermined distance, relying on the square latticed rules, this distance cannot be correctly determined unless two points are located on the same lattice line and the distance between these two points is equal to a value obtained by multiplying the interval of the lattice lines by a certain integer number. If a straight line is drawn no in parallel to the ruled lines, there are many cases that a length and a position can be hardly, correctly determined.
Also when a radius of a circle is designated, it is difficult to establish a correct designation unless the center of the circle is coincident with the latticed point.
As previously explained, the optimum shapes of the rules, optimum intervals thereof and optimum positions thereof should be determined based upon the sorts and target amounts of the processing operations to be executed, and there are some cases that the squared latticed rules impede the correct position designation.
It is so desirable that the display displays only such ruled lines as to be utilized when an operator performs an operation. For instance, if a distance is designated by using a lattice interval as a unit, a selectable point for the figure processing is included in the points on the lattice line which passes through the datum point used to measure the distance.
However, in accordance with the conventional figure processing apparatuses, since a large quantity of unnecessary points are displayed, there are higher probabilities that erroneous designation may happen to occur, because an operator moves his hand and causes visual errors.
Furthermore, there are some cases that no point is present t be designated by the operator in the latticed rules, when a radius cannot be designated unless a gradient of the latticed rules is modified because a lattice point indicative of the radius scales out from the display, or when a designation is made based on an angle.
Furthermore, there is only one sort of latticed rules which can be used at the same time. If the position, interval and angle of the latticed rules being displayed, are not suitable, the attributes of the rules must be changed. For example, in case that a plurality of ruled lines are alternately used, the attributes of the ruled lines must be changed every time. An operator must give up an operability of the conventional figure processing apparatus and a correct positional designation thereof, and thus he must continue to use the same ruled lines, or he endures such a cumbersome operation that the attributes are repeatedly changed.
Also, a ruled line is formed using a coordinate of at least one datum point as a reference point. For instance, latticed rules are formed so that coordinates of two datum points are used for opposite points of the unit lattice, whereas concentric ruled lines are formed and displayed in dot lines with a predetermined interval so that the center point is located at a coordinate of a datum point. To perform an enlarging process or a compressing process with respect to a figure drafted on a display screen with displaying an arbitrary ruled line thereon, there are some cases to easily draft a correct figure by substituting the presently displayed ruled lines by suitable ruled lines for an individual process.
For instance, when a circular figure is enlarged or reduced with fixing the center, it is preferable to use concentric ruled lines whose datum points are the center of the circular figure. However, it is difficult to designate the correct coordinate of this datum point with reference to the ordinary latticed rules and the displayed circular figure.